Inlet guide vanes are commonly used with centrifugal fans having fan wheels with backward inclined, air foil or flat blades. The inlet vanes impart a spin to the air such that it enters the fan wheel in the direction of rotation. This results in decreased air flow, lower static discharge pressure, and decreased brake horsepower requirements. Adjustment of the inlet vane angle provides modulation of air flow over a relatively broad range with substantial savings in operating costs when compared to other modulation techniques, such as use of discharge air dampers.
The prior art includes numerous designs for adjustable inlet guide vane mechanisms. Generally, all such devices provide means for simultaneously adjusting the inlet vanes between an extreme open position, allowing maximum air flow, and an extreme closed position, allowing a minimum air flow. The means for adjusting the vanes ideally should be infinitely variable, free of binding but without excessive "slop" or free-play, and of simple design and construction to avoid excessive manufacturing costs.
Inlet guide vane designs found in the prior art can generally be divided into two groups--those in which the inlet vanes are adjusted by means exterior to the hub, and those in which they are adjusted by means adjacent to the center of the inlet. Examples of the former group include inventions disclosed in U.S. Pat. Nos.: 2,435,092; 2,621,848; 2,827,224; 3,056,541; 3,566,916; and 4,177,007. Each of these patents shows an assembly with vanes fixedly mounted on shafts which at one end extend radially through an inlet cone or shroud. A crank arm is attached to the extending end of each shaft and connected to means for rotating the shafts with their attached vanes. Although the patents differ substantially in the apparatus disclosed for rotating the shafts, such means typically include a ring connected with a flexible joint or link assembly to each crank arm. An exception is the '541 patent, in which the crank arm of adjacent shafts are interconnected with links having a ball and socket joint at each end.
U.S. Pat. Nos. 2,063,174 and 4,187,879 describe examples of the latter group, in which the vanes are rotated about fixed shafts by means disposed adjacent a hub at the center of the inlet cone. In the '174 patent, a conical-shaped rotary member is journaled on the hub and has longitudinal grooves formed therein for receipt of a follower which extends from the root end of each vane; the hub is rotated to adjust all the vanes simultaneously.
The '879 patent shows an adjustment ring located at one side of a hub and concentric to the inlet cone. A crank arm extends from the root end of each vane at a very precise compound angle relative to the axis of the shaft. Each crank arm is connected to the adjustment ring with a single ball and socket joint. The socket member of this joint is square shouldered to fit a similarly shaped hole in the crank arm. As the adjustment ring is rotated, the ball rotates within the socket member and the socket slides back and fourth within the hole in the crank arm. The combined motion is apparently necessary to provide the required articulation to avoid binding as the vanes are adjusted.
Both the '879 and the '174 patent claim to provide a simple and inexpensive inlet vane adjustment mechanism; yet, each is somewhat complex and expensive to build, especially for use with smaller fans in light industrial air conditioning applications. For example, an expensive machining operation is required to produce the conical-shaped ring with the follower grooves shown in the '174 patent; likewise, in the '879 patent it is apparently necessary to form the crank arm at a complex angle with a precision of 0.5.degree., to avoid binding of the ball and socket joint as the vanes are moved. Since it is essential that manufacturing costs be extremely low to economically justify use of inlet vanes on smaller fans, the prior art does not appear to provide a sufficiently low cost design.
In consideration thereof, it is an object of this invention to provide an inlet guide vane mechanism which is both simple to manufacture and which uses relatively inexpensive parts.
It is a further object of this invention to provide means for simultaneously adjusting the inlet vanes of such an assembly without binding the moving parts thereof.
It is still a further object of this invention to provide such an assembly in which there is minimum vane free-play, and in which rotation of the vanes may be precisely effected.
These and other objects of the present invention will be apparent from the disclosure which follows and by reference to the attached drawings.